1. Field of the Invention
The present invention relates to the field of relaying within a frequency division duplexing (FDD) based cellular communications network designed for packet transmission. More specifically, the present invention is a method and apparatus involving a multi-hop transmission scheme utilizing intelligent relays to maximize coverage and capacity over a conventional cellular system designed for packet transmission.
2. Description of the Prior Art
Multi-hop relaying and ad-hoc networks are emerging as popular options to enhance the coverage performance of packet-based wireless networks. The basic idea of such networks is that the users in locations with poor wireless environments get their data from nearby wireless entities in the same cell, such as peer mobiles, moving vehicular devices, or devices at fixed locations, rather than directly from the serving base station. The entities that deliver the data to the end users are called relays. Relays perform communications between the base station and the end-users, or even between users. Some such multi-hop relaying and ad-hoc networks may exist even without centralized nodes such as base stations.
Known ad-hoc networking includes examples such as virtual personal distributed networks, interoperability with fixed/overlay networks, and multi-hop augmented infrastructure based networks. Virtual personal distributed networks involve standalone networks with capability for peer-to-peer connectivity that can also be connected to outer networks through a backbone gateway. Such a scenario is also called a pure-ad-hoc network 10 as seen in prior art FIG. 1 with peer-to-peer connections 11. Typical examples of such networks include military packet radio networks, personal area networks (PAN), network of sensors, home networks, vehicular networks, and wireless local area networks (WLAN) (as shown in FIG. 1 as element 12).
The second known example as shown in prior art FIG. 2 is the combination of ad-hoc networks with fixed/overlay networks. This can be regarded as a heterogeneous network 20 supporting dual air interfaces by a single user terminal, such as a WLAN 22 overlaid by a cellular network 21. The general coverage is given by the cellular network 21, with the addition (shown by link 23) of “hot spot” high data rate coverage by WLAN 22.
The third known example as shown in prior art FIG. 3 is basically a single air interface network 31 with coverage extension through relays sharing the resources in the same cell. This relaying can be performed either through peer terminals (“peer-to-peer relaying”) 32 or fixed nodes installed as a part of infrastructure (“fixed seeds relaying”) 33. If relaying were done through peer terminals, there would be several issues such as security and egoism. Basically, peer-to-peer relaying relies on using other terminal's power to deliver a specific user's data. Therefore, what portion of terminal battery power should be used for others would be a serious issue, both for technical and business reasons. Moreover, security is another concern in adopting peer-to-peer relaying. Infrastructure-based relaying such as fixed relay nodes would resolve these issues, but it requires additional cost to the system for many relay nodes
Infrastructure based fixed relays may be configured in various ways. They may exist in FDD mode or time division duplexing (TDD) mode and may utilize different spectrum for the base-relay link vs. the relay to user equipment (UE) link. In the FDD mode, they may employ the same FDD spectrum to minimize the transceiver hardware requirements. In this case, the need to share the FDD spectrum between the two links (BS-relay; relay—UE) results in a reduction in overall system capacity. Further, the interference caused by the relay nodes transmitting in the same frequency band as their peers as well as any needs of the base station (BS) required to be managed.
FIG. 4 illustrates the concept of conventional cellular 40 without a relay and illustrates the problem of providing uniform coverage to services with varying needs. In this case all time slots are allocated for BS-UE transmission 41, 42; however the efficiency of usage of the timeslots varies depending on the BS-UE link. Capacity is optimized by delivering data to the UE with the best rates, while also considering fairness in servicing UEs in the entire cell. This latter requirement impact the achievable capacity in that distant UEs require more timeslots to receive the same data at a lower rate.
FIG. 5 illustrates the conventional system 50 of multihop relaying. As shown by the transmission representation 51, 52, the available time slots are distributed between the BS and relays, with no facility to achieve simultaneous transmission, but showing the ability to increase the coverage over a conventional cellular system. In the basic assumption of the system, a fat pipe downlink with adaptive modulation and coding is used to enable communications for a range of services. No power control is employed (e.g., HSDPA). Scheduling and routing is performed at the BTS. Coverage may be improved but there is a potential aggregate capacity hit (at best no improvement) due to timeslots not being shared between the hops. However, it may be assumed that relays have on-overlapping transmit areas and are capable of simultaneous transmission.
What is needed therefore is an efficient, cost-effective multi-hop manner of FDD based relaying for eliminating the “coverage holes” within packet based cellular networks, while simultaneously optimizing capacity.